From 64f4e8555b67707d77b7c00584fb514f0da9869a Mon Sep 17 00:00:00 2001
From: Kshitij Sobti <kshitij@sobti.in>
Date: Thu, 4 Jan 2024 09:59:49 +0530
Subject: [PATCH] feat: Add support for Google Tag Manger This change adds
 support for Google Tag Manager along with some common options for Google Tag
 Manager.

---
 src/initialize.js                          |   4 +-
 src/scripts/GoogleTagManagerLoader.js      |  60 +++++++++++
 src/scripts/GoogleTagManagerLoader.test.js | 117 +++++++++++++++++++++
 src/scripts/index.js                       |   1 +
 4 files changed, 180 insertions(+), 2 deletions(-)
 create mode 100644 src/scripts/GoogleTagManagerLoader.js
 create mode 100644 src/scripts/GoogleTagManagerLoader.test.js

diff --git a/src/initialize.js b/src/initialize.js
index 2c7223595..a66fffce9 100644
--- a/src/initialize.js
+++ b/src/initialize.js
@@ -68,7 +68,7 @@ import {
 import {
   configure as configureAnalytics, SegmentAnalyticsService, identifyAnonymousUser, identifyAuthenticatedUser,
 } from './analytics';
-import { GoogleAnalyticsLoader } from './scripts';
+import { GoogleAnalyticsLoader, GoogleTagManagerLoader } from './scripts';
 import {
   getAuthenticatedHttpClient,
   configure as configureAuth,
@@ -290,7 +290,7 @@ export async function initialize({
   analyticsService = SegmentAnalyticsService,
   authService = AxiosJwtAuthService,
   authMiddleware = [],
-  externalScripts = [GoogleAnalyticsLoader],
+  externalScripts = [GoogleAnalyticsLoader, GoogleTagManagerLoader],
   requireAuthenticatedUser: requireUser = false,
   hydrateAuthenticatedUser: hydrateUser = false,
   messages,
diff --git a/src/scripts/GoogleTagManagerLoader.js b/src/scripts/GoogleTagManagerLoader.js
new file mode 100644
index 000000000..139a187df
--- /dev/null
+++ b/src/scripts/GoogleTagManagerLoader.js
@@ -0,0 +1,60 @@
+/**
+ * @implements {GoogleTagManagerLoader}
+ * @memberof module:GoogleTagManager
+ */
+class GoogleTagManagerLoader {
+  constructor({ config }) {
+    this.gtmId = config.GOOGLE_TAG_MANAGER_ID;
+    this.gtmArgs = '';
+    if (config.GOOGLE_TAG_MANAGER_AUTH) {
+      this.gtmArgs += `&gtm_auth=${config.GOOGLE_TAG_MANAGER_AUTH}`;
+    }
+    if (config.GOOGLE_TAG_MANAGER_PREVIEW) {
+      this.gtmArgs += `&gtm_preview=${config.GOOGLE_TAG_MANAGER_PREVIEW}`;
+    }
+    if (config.GOOGLE_TAG_MANAGER_ADDNL_ARGS) {
+      if (!config.GOOGLE_TAG_MANAGER_ADDNL_ARGS.startsWith('&')) {
+        this.gtmArgs += '&';
+      }
+      this.gtmArgs += config.GOOGLE_TAG_MANAGER_ADDNL_ARGS;
+    }
+  }
+
+  loadScript() {
+    if (!this.gtmId) {
+      return;
+    }
+
+    global.googleTagManager = global.googleTagManager || [];
+    const { googleTagManager } = global;
+
+    // If the snippet was invoked do nothing.
+    if (googleTagManager.invoked) {
+      return;
+    }
+
+    // Invoked flag, to make sure the snippet is never invoked twice.
+    googleTagManager.invoked = true;
+
+    googleTagManager.load = (key, args, options) => {
+      const scriptSrc = document.createElement('script');
+      scriptSrc.type = 'text/javascript';
+      scriptSrc.async = true;
+      scriptSrc.innerHTML = `
+      (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
+       new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
+       j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
+       'https://www.googletagmanager.com/gtm.js?id='+i+dl+'${args}';f.parentNode.insertBefore(j,f);       
+       })(window,document,'script','dataLayer','${key}');
+      `;
+      document.head.insertBefore(scriptSrc, document.head.getElementsByTagName('script')[0]);
+
+      googleTagManager._loadOptions = options; // eslint-disable-line no-underscore-dangle
+    };
+
+    // Load GoogleTagManager with your key.
+    googleTagManager.load(this.gtmId, this.gtmArgs);
+  }
+}
+
+export default GoogleTagManagerLoader;
diff --git a/src/scripts/GoogleTagManagerLoader.test.js b/src/scripts/GoogleTagManagerLoader.test.js
new file mode 100644
index 000000000..12022764c
--- /dev/null
+++ b/src/scripts/GoogleTagManagerLoader.test.js
@@ -0,0 +1,117 @@
+import { GoogleTagManagerLoader } from './index';
+
+const gtmId = 'test-key';
+
+describe('GoogleTagManager', () => {
+  let gtmScriptId;
+  let firstScriptTag;
+
+  beforeEach(() => {
+    window.googleTagManager = [];
+    document.head.innerHTML = '<title>Testing</title><meta charset="utf-8" /><script id="testing"></script>';
+    document.body.innerHTML = '<script id="stub" />';
+    gtmScriptId = `<script src="https://www.googletagmanager.com/gtm.js?id=${gtmId}" />`;
+  });
+
+  function loadGoogleTagManager(scriptData) {
+    const script = new GoogleTagManagerLoader(scriptData);
+    script.loadScript();
+  }
+
+  function setupConfigData(configVars) {
+    const data = {
+      config: {
+        ...configVars,
+      },
+    };
+    return data;
+  }
+
+  describe('with valid GOOGLE_TAG_MANAGER_ID', () => {
+    let data;
+    beforeEach(() => {
+      data = setupConfigData({ GOOGLE_TAG_MANAGER_ID: gtmId });
+      loadGoogleTagManager(data);
+      expect(global.googleTagManager.invoked)
+        .toBe(true);
+    });
+
+    it('should initialize google tag manager', () => {
+      expect(document.head.children[0])
+        .toContainHTML('<title>Testing</title>');
+      // The first inserted script tag should be the first script tag
+      // eslint-disable-next-line prefer-destructuring
+      firstScriptTag = document.head.getElementsByTagName('script')[0];
+      expect(firstScriptTag)
+        .toContainHTML(gtmScriptId);
+    });
+
+    it('should not initialize google tag manager twice', () => {
+      const scriptCountPre = document.head.getElementsByTagName('script').length;
+      loadGoogleTagManager(data);
+      const scriptCountPost = document.head.getElementsByTagName('script').length;
+      expect(scriptCountPost)
+        .toEqual(scriptCountPre);
+    });
+  });
+
+  describe.each([
+    {
+      tag: 'PREVIEW',
+      value: 'preview-xyz',
+      queryParam: 'gtm_preview=preview-xyz',
+    },
+    {
+      tag: 'AUTH',
+      value: 'auth-xyz',
+      queryParam: 'gtm_auth=auth-xyz',
+    },
+    {
+      tag: 'ADDNL_ARGS',
+      value: 'gtm_cookies_win=x',
+      queryParam: 'gtm_cookies_win=x',
+    },
+    {
+      tag: 'ADDNL_ARGS',
+      value: '&gtm_cookies_win=x',
+      queryParam: 'gtm_cookies_win=x',
+    },
+  ])('with other valid Google Tag Manager options', ({
+    tag,
+    value,
+    queryParam,
+  }) => {
+    it(`should correctly handle the GOOGLE_TAG_MANAGER_${tag} option`, () => {
+      const data = setupConfigData({
+        GOOGLE_TAG_MANAGER_ID: gtmId,
+        [`GOOGLE_TAG_MANAGER_${tag}`]: value,
+      });
+      loadGoogleTagManager(data);
+      // eslint-disable-next-line prefer-destructuring
+      firstScriptTag = document.head.getElementsByTagName('script')[0];
+      const scriptURL = new URL(firstScriptTag.src);
+      // Options shouldn't get merged.
+      expect(scriptURL.searchParams.size)
+        .toBe(2);
+      expect(scriptURL.search)
+        .toContain(queryParam);
+    });
+  });
+
+  describe('with invalid GOOGLE_TAG_MANAGER_ID', () => {
+    beforeEach(() => {
+      const data = setupConfigData({ GOOGLE_TAG_MANAGER_ID: '' });
+      loadGoogleTagManager(data);
+      expect(global.googleTagManager.invoked)
+        .toBeFalsy();
+    });
+
+    it('should not initialize google analytics', () => {
+      Array.from(document.head.getElementsByTagName('script')).forEach(scriptNode => {
+        expect(scriptNode)
+          .not
+          .toContainHTML(gtmScriptId);
+      });
+    });
+  });
+});
diff --git a/src/scripts/index.js b/src/scripts/index.js
index 3c627f0cc..b52b32e5b 100644
--- a/src/scripts/index.js
+++ b/src/scripts/index.js
@@ -1,2 +1,3 @@
 /* eslint-disable import/prefer-default-export */
 export { default as GoogleAnalyticsLoader } from './GoogleAnalyticsLoader';
+export { default as GoogleTagManagerLoader } from './GoogleTagManagerLoader';